Case study: monitoring of Glc4 tetrasaccharide in the urine of Pompe patients, use of MALDI-TOF MS, and 1 H NMR

Due to the lack of the acid 1,4-α-glucosidase, the urine of Pompe patients contains increased levels of specific glucose tetrasaccharide αGlc(1 → 6)αGlc(1 → 4)αGlc(1 → 4)Glc (Glc4), which was approved as a non-invasive biomarker of glycogen accumulation in the muscles of Pompe patients. MALDI-TOF mass spectrometry and 1 H NMR spectroscopy were used for Glc4 detection in the urine samples of four Pompe patients with infantile, juvenile, and adult forms of the disease, before and during, or before and after, enzyme replacement therapy. The increased sensitivity and decreased urine volume required for Glc4 detection by MALDI-TOF mass spectrometry was obtained by specific derivatization directly on the MALDI plate by 3-aminoquinoline. This method is a suitable and fast method for Pompe screening. 1 H NMR spectra, used for precise Glc4 quantifications, were proposed for the enzyme replacement therapy efficiency monitoring. Besides the clinical features and the biochemical parameters, knowledge about the evolution of the Glc4 levels over time during the administration of the therapy could help monitoring of the patient outcome as part of the standard protocol.